Elevator hoisting mechanism



United States Patent 3,174,585 ELEVATUR HGESTING MECHANISM Daniel DarioTofanelli, Bronxville, N .Y., assignor to Otis Elevator Company, NewYork, N.Y., a corporation of New Jersey Filed Aug. 13, 1962, Ser. No.216,455 Claims. (Cl. 187-42) The invention relates to hoisting mechanismfor elevators, especially to hoisting mechanism providing a tractiondrive for elevators.

In elevator traction drives, the elevator car and its counterweight areraised and lowered by means of the so-called traction machine which maybe located at the top or bottom of the elevator hoistway. Where arrangedat the bottom of the hoistway, the car and counterweight are suspendedby roping which pass over one or more idler sheaves at the top of thehoistway. The car and counterweight are driven by roping which extendsfrom the bottom of the car down and around the hoisting sheave and up tothe bottom of the counterweight. Such form of drive has many advantagesand the invention is directed to driving mechanism of this character.

With the hoisting mechanism located at the bottom of the lioistwa it isnecessary to assure suiiicient traction for the safe operation of theelevator. One such arrange ment which has been proposed is to extend thehoisting ropes from the bottom of the car around the bottom of thehoisting sheave, thence up and around a secondary sheave, back andaround the hoisting sheave and up to the counterweight. Such a ropingarrangement is known as double wrap traction. Springs exert forceupwardly on the secondary sheave to cause traction between the hoistingsheave and hoisting roping. However, as a result of expansion of thesprings to take up rope stretch, traction is decreased, necessitatingfrequent adjustments. Such an arrangement is disclosed in the patent toBaldwin No. 657,380, granted September 4, 1900. This applicationdescribes a related type of system and is a continuation-in-part of myapplication Serial No. 768,149, filed October 20, 1958, now abandoned.

One object of the invention is to provide an improved multi wraptraction drive at the bottom of the hoistway in which the traction isnot decreased with rope stretch.

Another object of the invention is to provide such a drive which alsoserves to release the traction should either the car or counterweightbottom in the hoistway.

Still another object of the invention is to provide such a drive whichalso serves to cushion the downward movement of the car or counterweightwhen its bottoms in the hoistway.

An additional object of the invention is to provide in such a drivesystem a braking arrangement operating directly on the idler sheavewhich supports the car and counterweight.

In carrying out the invention according to the preferred arrangement,the hoisting roping extends from the bottom of the car down around ahoisting sheave, up and around a secondary sheave, back around thehoisting sheave and up to the bottom of the counterweight, similar tothe above noted prior construction. The secondary sheave is mounted on acrosshead which is supported on fluid actuated mechanism. This mechanismcomprises, at each end of the crosshead, a piston upon which that end ofthe crosshead is mounted and which extends downwardly into a cylindersupported at the bottom of the hoistway. Fluid is supplied to thecylinders under a pressure to move the pistons upwardly tensioning theropes about sheaves and thus maintaining the desired available tractionbetween the hoisting sheave and hoist- Fatented Mar. 23, 1965 ingroping. Should bottoming of the car take place, it engages one end ofthe crosshead to move it downwardly. Thus the secondary sheave is moveddownwardly to release the traction. At the same time the piston at thatend of the crosshead is moved downwardly into its cylinder, cushioningthe downward movement of the car. At the same time a control is actuatedto release the pressure in the other cylinder to enable the crosshead tomove downwardly without canting. This brings the car to a stop andobivates pulling the counterweight into the overhead. Similarly, shouldbottoming of the counterweight take place, it engages the other end ofthe crosshead to move it downwardly. Thus the secondary sheave is moveddownwardly to release the traction. At the same time the piston at thatend of the crosshead is moved downwardly into its cylinder, cushioningthe downward movement of the car. At the same time a control is actuatedto release the pressure in the other cylinder to enable the crosshead tomove downwardly without canting. This brings the car to a stop andobviates pulling the counterweight into the overhead. Similarly, shouldbottoming of the counterweight take place, it engages the other end ofthe crosshead to move it downwardly. Thus the secondary sheave is moveddownwardly to release the traction. At the same time the piston at thisother end of the crosshead is moved downwardly into its cylinder,cushioning the downward movement of the counterweight. At the same timea control is actuated to release the pressure in the first cylinder toenable the who're crosshead to move downwardly without canting. Thisbrings the counterweight to a stop and obviates pulling the car into theoverhead.

A brake is operative directly on the overhead sheave which supports thecar and counterweight and is operated automatically should the pressuredecrease in either or both the cylinders beneath a predetermined valueor if the hoisting ropes break or stretch excessively such that tractionmight be lost.

Features and advantages will be seen from the above description andappendent claims.

In the drawings:

FIGURE 1 is a trimetric schematic representation of.

an elevator system with hoisting mechanism embodying the invention; and

FIGURE 2 is a simplified view in elevation, with parts in section, ofthe hoisting mechanism of FIGURE 1.

FIGURE 3 is a simplified view in elevation of an internal type of brakesuitable for use in the described embodiment.

Referring to the drawings, the elevator car It! and its counterweight 11are supported by roping 12 passing over an idler sheave 13 at the top ofthe hoistway. Hoist ing roping 15 is secured as at 16 to the bottom ofthe car and extends downwardly therefrom around the bottom of hoistingsheave 17. From the hoisting sheave, roping 15 extends upwardly andaround the top of secondary sheave 2i) and thence downwardly and againaround the bottom of the hoisting sheave, doublerope grooves beingprovided on the hoisting sheave for this purpose. From the hoistingsheave the hoisting roping extends upwardly too the bottom of thecounterweight where it is secured as at 21. This provides a double wraptraction drive.

The hoisting sheave .17 is driven by the hoisting motor 22 mounted onbed plate 23. The sheave shaft 24 is illustrated as supported at the endopposite the motor by a pedestal 25 mounted on bed plate 23. The shaft26 of the secondary sheave is mounted on a support in the form of acrosshead 27 extending at right angles to shafts 24 and 26 beyond thehoisting sheave on each side thereof. This crosshead may be in the formof two spaced channel members 30. The crosshead is supported at the leftend by a plunger 31 operating in a cylinder 32, and at the right end bya plunger 33 operating in a cylinder 34. The upper end 35 of plunger 31is open and is secured to the under side of a plate 36 in turn securedto the bottom of the crosshead. Plunger 31 may be actuated by anysuitable fluid such as air, water or oil and plate 36 has an opening 37therein to permit escape of this fluid. The same arrangement is providedfor the other end of the crosshead.

In this described embodiment air is the preferred medium and air underpressure is supplied to the cylinders by a compressor with accumulatortank (not shown). This enables a constant regulatable pressure to beprovided. A pipe 40 leads from the pressure supply and connects throughcheck valve 41 to cylinder 32 and by way of pipe 42 to cylinder 34.Relief valves 43 and 44 may be solenoid actuated subject to the controlof switches 45 and 46 respectively, mounted at opposite ends of thecrosshead. A pressure relief valve 47 is arranged in the lower end ofplunger 31 and a similar valve is provided for plunger 33. A buffer 50is customarily provided at the bottom of the hoistway. If the car runsinto the hoistway pit the plunger 51 of the buffer is engaged by thebottom of the car to cushion downward movement of the car and finallybring it to a stop. A similar buffer 52 is provided for thecounterweight and has a plunger 53 adapted to be engaged by the bottomof the counterweight.

As a part of the braking arrangement pressure switch 74 is connected tocylinder 32 and is arranged such that its contacts are actuated when thepressure within the cylinder decreases below a predetermined value.These contacts are connected by the indicated conductors into thecircuit of the coil of brake solenoid 66 (FIG. 3). On the left end ofchannel members 30 (FIG. 2) which support secondary sheave 20 there isfastened a cam 68 of suitable length and in position to cooperate withcam follower or roller 72 of limit switch 70. The contacts (not shown)of switch 7 are connected over the conductors indicated into the circuitof the coil of brake solenoid 66 (FIG. 3). If perchance hoisting ropes15 should break or should stretch beyond the expansion capabilities ofplunger 31 in cylinder 32 (see plunger stop 54) crosshead 27 will beforced upwardly to a position where roller 70 runs off of cam 68 toactuate the contacts of switch 70.

In FIG. 3 there is shown in simplified form an expanding type,internally mounted brake having brake shoes 60, 62 which uponinterruption of current in brake solenoid or magnet 66 are applied bysprings 64. Similarly, when the proper amount of current flows in brakemagnet 66 its cores are retracted to overcome the pressure of thesprings and retract the shoes.

Mounted integral with idler sheave 13 at the top of the hoistway is abrake 56 of the type just described. The contacts of pressure switch 74and limit switch 70 are connected in the circuit of its brake solenoidcoil along with any other contacts appropriate in a conventional controlsystem such that brake 56 is actuated to release its brake shoes 60, 62against the brake drum whenever a stop is made at a landing or ifpressure in cylinder 32 decreases dangerously or ropes break or stretchexcessively.

A brake 58 may, optionally, be provided integral with hoisting sheave 17or be mounted immovably on sheave shaft 24. If so provided, the coil ofits brake magnet 66 will be actuated in the same manner and at the sametime as has previously been explained for the overhead brake 56.

Although it has not been shown in detail it is to be understood thatappropriate control circuits, of which several conventional designs areavailable, are to be provided for the actuation of the brake mechanismor mechanisms. Thus either or both brakes may be applied at each landingstop (assuming both upper and lower brakes 56, 58 are supplied) byinterruption of the circuit for energizing the coil of each brake magnet66, If only one brake mechanism is to be supplied it is preferable thatit be brake 56 associated with overhead sheave 13in which case it willbe actuated by the conventional control circuit at each landing stop aswell as by pressure switch 74 or limit switch 70 when these areactuated. The actuating circuit will, of course, include wires a and bof limit switch 70 and wires c and d of pressure switch 74 in seriesconnection with wires e and f of the coil of brake magnet 66.

In operation, the air supplied to'cylinders 32 and 34 forces plungers 31and 33 respectively upwardly to place tension in the hoisting roping 15.The air pressure is adjusted so as to provide the desired availabletraction between driving sheave 17 and hoisting roping 15it beingunderstood this traction increases as the tension in the ropes isincreased. As the air pressure falls due to leakage, the check valve 41allows more air to be supplied to the cylinders to maintainsubstantially constant pressure. Should the car bottom, that is, runpast the lowermost floor into the hoistway pit, it strikes the plunger51 of buffer 50 which acts to exert a gradually retarding action. Asdownward movement of the car continues, it engages the left end ofcrosshead 27 and acts therethrough to force plunger 31 downwardly incylinder 32 against the air pressure therein. Relief valve 47 acts tolet go when the pressure builds up to a certain value to permit some ofthe entrapped air to escape at the top of the plunger. The ensuing dropin pressure causes switch 74 to open its contacts in the circuit of thecoil of brake magnet 66 of the overhead brake 56, and of machine brake58 if provided. At the same time the car actuates switch 46 to causeactuation of valve 44 to allow the escape of air from cylinder 34, thusenabling plungers 31 and 33 to move downwardly as a unit and thusobviate canting of the crosshead. The downward movement of thecrosshead, by decreasing the distance of the secondary sheave from thehoisting sheave, releases the traction of the hoisting ropes, preventingroping 12 pulling the counterweight into the overhead. Also the downwardmovement of plunger 31 assists bufier Sit in bringing the car to a stop.A similar action takes place in case of bottoming of th counterweight.

While the invention has been illustrated as applied to an installationin which buffers 50 and 52 are provided, it is to be understood thatthese buffers may be omitted and the retarding action obtained by theplungers 31 and 33 in cylinders 32 and 34. In the latter case theplungers would be arranged to provide a gradually increasing retardingaction as is understood in the buffer art. Where used in conjunctionwith butters, it has the advantage that it may be applied to existinginstallations in which buffers are provided.

The invention has been described as utilizing a double Wrap tractiondrive. Other multi wrap traction drives, such for example as triplewrap, may be utilized. The greater number of wraps has the advantagethat it enables the desired traction to be obtained with lower pressurein the cylinders. It is preferred to provide a minimum amount oftraction which will prevent slip. This further reduces the pressure inthe cylinders. Low pressure in the cylinders is of advantage in that itincreases rope life. Also, a multi wrap drive utilizing V belts, such asthose with steel centers, and V grooves in the driving and secondarysheaves, may be used instead of roping, thereby lowering the pressure inthe cylinders required for the desired traction.

As many changes can be made in the above described construction and manyapparently diiferent embodiments of this invention can be made withoutdeparting from the scope thereof, it is intended that all mattercontained in the above description or shown on the accompany-ing drawingbe interpreted as illustrative only and not in a limiting sense.

What is claimed is:

1. In an elevator system in which the elevator car and its counterweightare suspended by roping passing over an idler sheave at the top of thehoistway, hoisting mechanism for the car and counterweight comprising, ahoisting sheave located at the bottom of the hoistway, a secondarysheave positioned above the hoisting she-ave and movable verticallyrelative thereto, hoisting roping extending from the bottom of the cararound the hoisting sheave, thence around the secondary sheave, backaround the hoisting sheave and up to the bottom of the counterweight,fluid actuated mechanism including a secondary sheave support supportingthe secondary sheave for exerting force thereon to move it upwardly withrespect to the hoisting sheave to provide traction between the hoistingroping and hoisting sheave, means for supplying fluid to said fluidactuated mechanism at a pressure to cause sufiicient tension in thehoisting roping to insure the desired amount of said traction,notwithstanding stretching of the roping, and means responsive todownward force exerted by the car on the secondary sheave support toactuate the fluid actuated mechanism to reduce the distance between thesecondary sheave and hoisting sheave to release the traction.

2. In an elevator system in which the elevator car and its counterweightare suspended by roping passing over an idler sheave at the top of thehoistway, hoisting mechanism for the car and counterweight compris ing,a hoisting sheave located at the bottom of the hoistway, a secondarysheave positioned above the hoisting sheave and movable verticallyrelative thereto, hoisting roping extending from the bottom of the cararound the hoisting sheave, thence around the secondary sheave, backaround the hoisting sheave and up to the bottom of the counterweight,fluid actuated mechanism including a secondary sheave support supportingthe second ary sheave for exerting force thereon to move it upwardlywith respect to the hoisting sheave to provide traction between thehoisting roping and hoisting sheave, means for supplying fluid to saidfluid actuated mechanism at a pressure to cause suflicient tension inthe hoist ing roping to insure the desired amount of said traction,notwithstanding stretching of the roping, and means responsive todownward force exerted by the counterweight on the secondary sheavesupport to actuate the fluid actuated mechanism to reduce the distancebetween the secondary sheave and hoisting sheave to release thetraction.

3. In an elevator system in which the elevator car and its counterweightare suspended by roping passing over an idler sheave at the top of thehoistway, hoisting mechanism for the car and counterweight com-prising,a hoisting sheave located at the bottom of the hoistway, a secondarysheave positioned above the hoisting sheave and movable verticallyrelative thereto, hoisting roping extending from the bottom of the cararound the hoisting sheave, thence around the secondary sheave, backaround the hoisting sheave and up to the bottom of the counterweight,fluid actuated mechanism including a secondary sheave support supportingthe secondary sheave for exerting force thereon to move it upwardly withrespect to the hoisting sheave to provide traction between the hoistingroping and hoisting sheave, means for supplying fluid to said fluidactuated mechanism at a pressure to cause sufficient tension in thehoisting roping to insure the desired amount of said traction,notwithstanding stretching of the roping, and means esponsive todownward force exerted by the car or counterweight on the secondarysheave support to actuate the fluid actuated mechanism to reduce thedistance between the secondary sheave and hoisting sheave, releasing thetraction, and to cushion further downward movement of the actuating caror counterweight.

4. In an elevator system in which the elevator car and its counterweightare suspended by roping passing over an idler sheave at the top of thehoistway, hoisting mechanism for the car and counterweight comprising, ahoisting sheave located at the bottom of the hoistway, a secondarysheave positioned above the hoisting sheave and movable verticallyrelative thereto, hoisting roping extending from the bottom of the cararound the hoisting sheave, thence around the secondary sheave, backaround the hoisting sheave and up to the bottom of the counterweight, asupport for the secondary sheave extending oppositely therefrom, a pairof cylinders, each having a plunger, one of said cylinders and itsplunger being positioned under one end of said support and the othercylinder and its plunger being positioned under the other end of saidsupport, said support being mounted on the upper ends of said plungers,and said cylinders being adapted upon the supply of fluid thereto to actthrough said plungers to exert force on said secondary sheave to move itupwardly with respect to the hoisting sheave and thus provide tractionbetween the hoisting roping and hoisting sheave, and means for supplyingfluid to said cylinders at a pressure to cause sufl'icient tension inthe hoisting roping to insure the desired traction, notwithstandingstretching of the roping, said sup port being positioned in the path ofdownward movement of both said car and counterweight to be engagedthereby upon the bottoming thereof to move said support downwardly torelease the traction.

5. In an elevator system in which the elevator car and its counterweightare suspended by roping passing over an idler sheave at the top of thehoistway, hoisting mechanism for the car and counterweight comprising, ahoisting sheave located at the bottom of the hoistway, a secondarysheave positioned above the hoisting sheave and movable verticallyrelative thereto, hoisting roping extending from the bottom of the cararound the hoisting sheave, thence around the secondary sheave, backaround the hoisting sheave and up to the bottom of the counterweight, asupport for the secondary sheave extending oppositely therefrom, a pairof cylinders, one at each end of the support, each cylinder having aplunger for supporting said support, said cylinders being adapted uponthe supply of fluid thereto to act through said plungers and support toextert force on said secondary sheave to move it upwardly with respectto the hoisting sheave and thus provide traction between the hoistingroping and hoisting sheave, means for supplying fluid to said cylindersat a pressure to cause suflicient tension in the hoisting roping toinsure the desired traction, notwithstanding stretching of the roping,one end of said support being positioned in the path of downwardmovement of said car to be engaged thereby upon the bottoming thereof tomove that end of said support downwardly to release the traction and theother end of said support being positioned in the path of downwardmovement of said counterweight to be engaged thereby upon the bottomingthereof to move that end of said support downwardly to release thetraction, and control means on each end of the support adapted uponoperation to relieve the fluid pressure in the cylinder under the otherend of the support, said control means on said one end being operable bythe car upon that end being engaged by the car, and said control meanson said other end of said support being operable by the counterweightupon. that end being engaged by the the counterweight.

6. In the elevator system in which the elevator car and itscounterweight are suspended by roping passing over an idler sheave atthe top of the hoistway, hoisting mechanism for the car andcounterweight comprising, a hoisting sheave located at the bottom of thehoistway, a secondary sheave positioned above the hoisting sheave andmovable vertically relative thereto, hoisting roping extending from thebottom of the car around the hoisting sheave, thence around thesecondary sheave back around the hoisting sheave and up to the bottom ofthe counterweight, a crosshead upon which the secondary sheave ismounted, a pair of cylinders, one at each end of the j crosshead, eachcylinder having a plunger for supporting the crosshead, said cylindersbeing adapated upon the supply of fluid thereto to act through saidplungers to exert force on said crosshead to move said secondary sheaveupwardly with respect to the hoisting sheave and thus provide tractionbetween the hoisting roping and hoisting sheave, means for supplyingfluid to said cylinders at a pressure to cause sufiicient tension in thehoisting roping to insure the desired traction, notwithstandingstretching of the roping, one end of said crosshead being positioned inthe path of downward movement of said car to be engaged thereby upon thebottoming thereof to move that end of said crosshead downwardly to release the traction and the other end of said crosshead being positionedin the path of downward movement of said counterweight to be engagedtherebyj upon the bottoming thereof to move that end of said crossheaddownwardly to release the traction, control means on each end of thecrosshead adapted upon operation to relieve the fluid-pressure in thecylinder under the other end of the crosshead, said control means onsaid one end being operable by that end being engaged by the car, andsaid control means on said other end of said sup port being operable bythat end being engaged by the counterweight, and a pair of butters, onefor the car and one for the counterweight, for cushioning the downwardmovement thereof, said crosshead being engaged to bring thecorresponding cylinder and plunger into action to as sist the acuatedbutter as the continued downward movement of the actuating car orcounterweight takes place.

7. In an elevator system in which the elevator car and its counterweightare suspended by roping passing over an idler sheave at the top of thehoistway and in which motive power is applied to the car and itscounterweight from hoisting mechanism located at the bottom of thehoistway, a powered hoisting sheave and a secondary sheave located atthe bottom of the hoistway said secondary sheave being positioned abovethe hoisting sheave and movable vertically relative thereto, hoistingroping extending from the bottom of the car around the hoisting sheave,thence around the secondary sheave, back around the hoisting sheave andup to the bottom of the counterweight, fluid actuated mechanismincluding a support for said secondary sheave for exerting force on saidsupport moving the secondary sheave upwardly with respect to saidhoisting sheave and tightening said ropes around said sheaves to provideavailable traction between the hoisting roping and hoisting sheave,means for supplying fluid to said fluid actuated mechanism at a pressureto cause suflicient tension in the hoisting ropes to provide the desiredamount of available traction, means responsive to downward force exertedby the car or its counterweight on the secondary sheave support todecrease the pressure of the fluid in said fluid actuated mechanism, aspring applied magnetically released mechanical brake mounted integrallywith said idler sheave .to control its rotation and pressure responsivemeans responsive to the decreased pressure in said fluid actuatedmechanism and operative to cause said brake to be applied to arrest therotation of said car supporting idler sheave.

8. In an elevator system in which motive power is' applied to theunderside of the car and the underside of its counterweight by ahoisting machine located at the bottom level of the hoistway, an idlersheave supported at the top of the hoistway over which the supportingropes between car and counterweight pass, a mechanical brake operativelyconnected when actuated to control the rotation of said sheave, the saidhoisting mechanism including a hoisting sheave and a secondary sheavepositioned thereabove and movable vertically relative thereto, hoistingroping extending from the bottom of the car around 7 the hoisting sheaveup and around the secondary sheave and back around the hoisting sheavethence up to the underside of the counterweight, fluid actuatedmechanism including a movable support for said secondary sheave exertingforce on said support to move said secondary sheave upwardly withrespect to the hoisting sheave thereby to increase the tension in thehoisting ropes, a limit switch connected to said sheave support andresponsive to upward movement of said support beyond a predeterminedposition, means for supplying to said fluid actuated mechanism fluid ata pressure to produce the desired rope tension notwithstandingstretching of the roping, means responsive to downward force exerted bythe car or its counterweight on the secondary sheave support to actuatethe fluid actuated mechanism to reduce the distance between the hoistingand secondary sheaves thereby releasing the traction, and meansconnecting said limit switch in the actuating control of said brakewhereby said brake is applied to check the rotation of said carsupporting idler sheave whenever said fluid actuated mechanism forcessaid secondary sheave support beyond said predetermined position.

9. In an elevator system in which the elevator car and its counterweightare suspended by roping passing over an idler sheave rotativelysupported at the top of the hoistway and in which motive power isapplied to the underside of said car and the underside of saidcounterweight by hoisting ropes powered by a hoisting machine located atthe lowest level of said hoistway, said hoisting machine including ahoist sheave and a secondary sheave positioned thereabove and movablevertically relative thereto, said hoisting ropes extending under thehoist sheave, up and over the secondary sheave thence back under thehoisting sheave before passing upwardly for connection to said car andcounterweight, the improvement which includes a mechanically-appliedbrake on said overhead idler sheave, a fluid actuated mechanismincluding a movable support for said secondary sheave for exerting forcethereon upwardly to separate said sheave from said hoisting sheavethereby producing tension in said hoisting ropes and available tractionfor movement of said car and counterweight, means for supplying fluidunder controlled pressure to said mechanism, means responsive todownward force exerted by the car or its counterweight on the secondarysheave support to reduce the separation of said hoisting and secondarysheaves to release the traction, and brake control means responsive bothto fluid pressure less than a predetermined value within said fluidactuated mechanism or separation of said hoisting and secondary sheavesbeyond a predetermined amount and operative to cause said brake to applyand arrest rotation of said car supporting idler sheave upon thepressure decreasing below said value or the sheave separation exceedingsaid predetermined amount.

10. In an elevator system in which the elevator car and itscounterweight are suspended by roping passing over an idler sheaverotatively supported at the top of the hoistway and in which hoistingpower is supplied from a hoisting machine located at the lowest level ofsaid hoistway by roping attached to the undersides of said car andcounterweight, said hoisting machine including a poweredhoisting sheaveand a vertically movable sec ondary sheave positioned thereabove, saidhoisting ropes extending from the connection to said car, under saidhoisting sheave, up and over said secondary sheave, down and under saidhoisting sheave and up to the connection to said counterweight, thearrangement which includes a mechanically applied brake on the overheadidler sheave, fluid actuated mechanism responsive to fluid supplied itunder controlled pressure and including a vertically movable support forsaid secondary sheave operative to exert force thereon upwardly andeffect desired vertical separation of said hoisting and secondarysheaves, pressure responsive means operative to its actuated state byinsufficient fluid pressure within said fluid actuated mechanism,positional means operative to its actuated state by excessive elevationof said movable secondary sheave support and an electrical controlcircuit efiective when energized to restrain the application of saidmechanically applied brake, said control circuit including said pressureresponsive means and said positional responsive means whereby theenergization of said circuit and the restraint on said mechanicallyapplied brake is interrupted by the actuation of either of said lastmentioned means in response to the decrease in said fluid pressure orthe elevation of said sheave support beyond predetermined limits,Whichever first occurs.

References Cited in the file of this patent UNITED STATES PATENTSBaldwin et a1. Sept. 4, 1900 Hymans Ian. 3, 1928 Palm -1 May 31, 1932Hymans Ian. 20, 1942 Margles Jan. 9, 1951 Wilbur June 25, 1957 BrandonFeb. 9, 1960

1. IN AN ELEVATOR SYSTEM IN WHICH THE ELEVATOR CAR AND ITS COUNTERWEIGHTARE SUSPENDED BY ROPING PASSING OVER AN IDLER SHEAVE AT THE TOP OF THEHOISTWAY, HOISTING MECHANISM FOR THE CAR AND COUNTERWEIGHT COMPRISING, AHOISTING SHEAVE LOCATED AT THE BOTTOM OF THE HOISTWAY, A SECONDARYSHEAVE POSITIONED ABOVE THE HOISTING SHEAVE AND MOVABLE VERTICALLYRELATIVE THERETO, HOISTING ROPING EXTENDING FROM THE BOTTOM OF THE CARAROUND THE HOISTING SHEAVE, THENCE AROUND THE SECONDARY SHEAVE, BACKAROUND THE HOISTING SHEAVE AND UP TO THE BOTTOM OF THE COUNTERWEIGHT,FLUID ACTUATED MECHANISM INCLUDING A SECONDARY SHEAVE SUPPORT SUPPORTINGTHE SECONDARY SHEAVE FOR EXERTING FORCE THEREON TO MOVE IT UPWARDLY WITHRESPECT TO THE HOISTING SHEAVE TO PROVIDE TRACTION BETWEEN THE HOISTINGROPING AND HOISTING SHEAVE, MEANS FOR SUPPLYING FLUID TO SAID FLUIDACTUATED MECHANISM AT A PRESSURE TO CAUSE SUFFICIENT TENSION IN THEHOUSING ROPING TO INSURE THE DESIRED AMOUNT OF SAID TRACTION,NOTWITHSTANDING STRETCHING OF THE ROPING, AND MEANS RESPONSIVE TODOWNWARD FORCE EXERTED BY THE CAR ON THE SECONDARY SHEAVE SUPPORT TOACTUATE THE FLUID ACTUATED MECHANISM TO REDUCE THE DISTANCE BETWEEN THESECONDARY SHEAVE AND HOISTING SHEAVE TO RELEASE THE TRACTION.